OK,I was helping my uncle pull a 454 out of a 79 c30 dually.We got it out.Now we were gonna put a 87 HO 305 in its place to sell it.Well the truck has a TH400 w/ the large converter pattern.The block is drilled for either starter head.So just swap to the 168 tooth large pattern flexplate right.WRONG!!!!!The new block has a smaller crank bolt pattern.Now what?????
Do the 86-up 350s have a 168 tooth dual converter pattern flexplate???Is it the small crank pattern like the 305????
I never knew they changed the flexplates too.

The small blocks went to a one piece rear main seal in 86. Flexplate for one piece rear seal is different. I had to buy a 'plate for an 87 350 700R4 truck, and it was around $65 at the local autoparts store. Don't know if they are drilled to take the TH400 convertor.

Sorry 78 Monte, that was news to me too. It seems Chevy has been playing havoc with many small details of the Chevy engine line in the search for compactness and of course things for the engineers to do. Crankshaft flywheel bolt patterns, pulley backspacings, water pump snouts you name it I doubt you could go into the store today and just say Chevy SB waterpump and only have two choices. Today it would be at least 10 maybe more. At one time SBC meant interchangeability but that day is slowly coming to an end. Ever try to buy a serpentine belt nowadays, an exercise in futility unless you have the original in your hand. I am not surprised your swap didn't go as planned.

Yea I'm still trying to accept the center bolt valve covers.Then they spring that on me.I never had a new S/B,now I don't think I ever want one.And was there a real reason for changing the center intake bolts,besides bordum???

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